Traffic actuated control system



Feb. 27, 1940. H. A. WILCOX 21,377

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Original Filed April 15, 1936 5 Sheets-Sheet 1 ATTORNEYS H. A. WILCOX Feb. 27, 1940.

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Original Filqd April 15. 1936 5 Sheets-Sheet 2 x cmu argyle m w W E 0 MM a i 5 Sheets-Sheet 3 I IN VEN TOR HAPPY ,4. W/LC'OX A TTOR/VE Y5 H. A. WILCOX Original Filed April 15, 1956 Feb. 27, 1940.

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS H. A. WILCOX Feb. 27, 1940.

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Original Filed April 15, 1936 5 Sheets-Sheet 4 IN VEN TOR HAPPY A. W/Lwx Mala" M 2 A TTORNEYJ H. A. WILCOX Feb. 27, 1940.

TRAFFIC ACTUATED CON 'I'ROL SYSTEM AND APPARATUS Original Filedjpril 15, 1936 5 Sheets-Sheet s m r N N R E 0 Wm H W e which the go" Reissued Feb. 27, 1940 PATENT OFFICE TRAFFIC AUI'UATED CONTROL SYSTEM AND APPARATUS Harry A. Wilcox, Norwalk,

Automatic Signal Corporation, New York, N. Y.,

Original No. 2,183,780, dated December 19, 1989,

Serial No. 74,422, April 15,

1936. Application for reissue December 28,1939, Serial No. 311,890

23 Claims. (Cl. 177-337) This invention relates to a trafiic system capable of use at the intersection of two trafiic lanes or streets, and has for its general object to provide an automatic system by means of which trafiic will be expeditiously and safely handled. This system is to a large extent controlled by the trafiic along the intersecting lanes. Its operation will be responsive not only to the presence of trafiic but will be affected also by the density of traflic in each lane. Previous systems to my knowledge have provided for tramc actuation of the signals but have less completely taken into account the element of the relative density of trafiic in the two lanes when tramc is very heavy.

The vehicle actuated trafiic control is not in itself a new invention, such systems having been in general use for'some' time. Previous systems have served admirably to control tramc at the intersection of two lanes when trafilc is light in one lane and heavy in the other, or when trailic is irregularly spaced in one or both of said lanes, but they have not been adapted so well to the most efiicient handling of intersections where trafiic is continuously heavy in both lanes. A system to be eflective under this latter condition must be sensitive to slight difference between two heavy traflic fiows.

The system disclosed herein handles efliciently any type of trafiic but is especially effective in handling heavy trafiic with the utmost efiiciency. This system is of the type in which within a maximum limit each vehicle approaching the intersection on a "go" signal after an initial interval which is preferably inserted as described below extends the period of display of such signal for a time after its approach, such time being designated as a vehicle protection period, right of way extension period, or vehicle interval.

Unlike the prior systems of this type the vehicle interval in this new system is decreased in accordance with the number of vehicles awaiting on the cross lane. Hence, of vehicles waiting on the cross lane, each vehicle entering the intersection from the lane in signal is being displayed is allotted a shortened time period for its passage. As a result of this fact a shorter spacing between vehicles in the moving line will yield the right of way. Therefore under the system disclosed herein a large number of waiting vehicles is more efi'ective than a small number to cause transfer of the right of way to the lane in which they are waiting. This invention therefore provides a system in which the right of way tends to revert more quickly to the lane having the trafiic control system, includes with a large group,

denser tramc thereby providing for maximum efiiciency in handling heavily travelled intersections where efiiciency is of the greatest importance. In effect it provides means whereby waiting traflic is able to exert a forcing effect to obtain the right of way sooner in accordance with its demand.

This system, like previous vehicle actuated t p and g signals to be displayed in each traific lane entering an intersection, a control mechanism to operate the stop and go" signals, and traffic detectors located in the aforementioned trafiic lanes, which effect the operationv of the control mechanism in such a manneras to cause the signal display periods to conform to the require-- ments of the tramc approaching the intersection. In this system as in the prior types of vehicle actuated systems the actuation of a trafiic detector in a traffic lan in which the stop signal is being displayed causes the right of way to be transferred to that lane at the first opportunity. If there is no trafiic entering the intersection from the lane in which the "go signal is being displayed a caution signal is usually immediately displayed in said lane and after a short period the right of way is transferred to the lane in which the stop" signal was being displayed.

If trafllc is moving in the lane wherein the llgo" the trafiic detector in the lane in which the signal is being displayed causes the right of way to be transferred thereto at the first break of a predetermined time in the said moving trafiic. If no such break occurs in said moving traific the right of way will be transferred at the end of a predetermined maximum period usually provided by a diii'erent timing element.

In this system as in previous systems, the actuation of a trafiic detector during the period in which the "go signal is being displayed to the lane wherein said trafiic detector is located causes such signal period to be extended under certain conditions. The go" periods for each traffic lane is divided into two parts. During the first part of this period the actuation of the trafllc detector in the lane in which the "go signal is being displayed is of no effect. This first part of the go period, called the initial interval", is introduced to allow time for standing trafiic to get into motion. While not essential to operation this initial interval is preferably introduced to increase the efiic'lency of the system. After the expiration of the initial interval the "go" signal will continue to be displayed for an interval of time at least sufficient for a moving vehicle to progress from the traflic detector thru the intersection. This last named interval has been identified above as the vehicleinterval". During the vehicle interval" the actuation of a traiilc detector in the lane in which the "go signal is being displayed extends the right of way period therein for a time interval reasonably sufficient to allow the vehicle which actuated the traflic detector to progress from said detector thru the intersection.

The system disclosed herein however includes a new and important feature in that the timing of the vehicle interval is affected by the number of waiting vehicles in the cross lane as mentioned before so that as the group of waiting vehicles increases in number the control will take advantage of shorter and shorter breaks in the moving tramc to transfer right of way to these waiting vehicles.

Furthermore this system includes another new feature in that it provides that if desired certain forms of trafflc such as trolley cars, fire apparatus, etc., to which it may be advisable to accord preferred treatment can thru actuating special detectors have the same effect on the timing of the signals as several ordinary vehicles.

This system, like some previous traiilc actuated systems is arranged so that the timing of the initial interval", the first part of the "go" period, can, before the beginning of said "initial interval, be preadjusted between a predetermined minimum value and a predetermined maximum value, by successive actuations of the traffic detector in the lane in which the "stop" signal is being displayed so that when said lane shall next be given the go signal the initial interval" of said "go signal display period will be timed in conformance with the volume of the traflic waiting in said lane, to the end that a large number of waiting vehicles will be granted a longer initial interval than will be granted to a small number. However in the system described herein the variable initial interval is achieved by a method using simpler and more reliable equipment than that used in previous systems, as will be more specifically shown later.

In this system the traflic detectors can be located at a distance from the intersection cus tomaryin the prior systems but it is entirely feasible, especially if the variable initial interval is employed, to locate them considerably farther from the intersection (two or three hundred feet or more for .example) thereby facilitating the counting of larger numbers of waiting vehicles which will increase the effectiveness of traffic approaching a stop signal in controlling the signal timing.

With the system adjusted to give a pronounced reduction of the vehicle interval after the accumulation of a certain amount of traflic approaching a stop signal a considerable degree of coordination between adjacent intersections can be obtained solely by the pressure of traflic itself without any electrical interconnection since the effect of a group of vehicles approaching successive intersections equipped with this system will be to so reduce the vehicle interval for cross traflic at each intersection as at any time subsequent to the cross street initial interval to practically seize the right of way at intersection after intersection thereby favoring uninterrupted progress to a sufficiently large compact group of vehicles.

Cross traffic will however be protected against unreasonable interruption since the cross street initial interval is timed in advance in accordance with the number of vehicles waiting on the cross street and is not reducible by main highway traffic, and in addition either a maximum limit to right of way on the main highway or a reduction of the main highway vehicle interval by accumulation of waiting cross street trafllc', or both, serve to protect the cross street trafllc.

The coordination effect outlined above will be obtained by a compact group of vehicles whether they move along one street or follow an irregular path through an area which is a considerable advantage over prior non-vehicle actuated coordinated systems in which coordination was necessarily arranged to favor the passage of traffic along a predetermined route.

Under this system while a compact group of vehicles is crossing its path, scattered tramc is automatically given the opportunity to come into close order through a natural accumulation. Hence when this system is applied to a large area constituting a grid of individually and independently controlled intersections trafllc will form into compact groups at the outlying intersections and then pass thru the grid as favored units thereby causing the controls throughout the whole area to function as a coordinated grid system without the necessity-for any electrical interconnection between intersections.

It will be appreciated that tramc is often heavier inbound toward the central area of a city in the morning and heavier outbound in the afternoon, and that in such cases the automatic natural coordination effect above noted with this invention will be particularly pronounced on the main traffic arteries.

It is an object of this invention to provide an improved traiiic control system wherein the functioning of the apparatus will automatically take into account the relative densities of traflic in the two roadways in determining the signal timing.

Another object is to provide an improved systern in which the denser traffic is favored, but in which the right of a single vehicle or a scattered group of vehicles to pass the intersection is not by any means permanently withheld. A single waiting vehicle will be given an opportunity to pass within a reasonable period after its approach to the intersection even though moving cross traflic may be continuous. If there is no cross traffic such a vehicle will be given the right of way immediately upon its approach.

It is another object to provide a system in which vehicles awaiting the right of way in one lane will facilitate yielding the right of wayfrom the other roadway by reducing the time allotted to each vehicle entering the intersection from such other roadway.

It is a further object to provide a system in which vehicles awaiting the right of way in one roadway will reduce substantially. in proportion to the number, of said waiting vehicles, the time allotted to each vehicle entering the intersection from the other roadway in which the go signal is being displayed thereby automatically permitting a large amount ofwaiting traiiic to take the right of way more easily, than a small amount.

It is also an object of the invention under some conditions to reduce substantially the vehicle protection interval on one street after suflicient traffic has accumulated on the opposite street.

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invention including timing apparatus with con- It is another object of this invention to proide a system in which waiting tramc will automsticauy and substantially in proportion to its volume prcadjust, by controlling the starting point, the timing of the following preliminary right of way period.

It is a further object to provide a system in which waiting traffic will automatically and substantially in proportion to its volume preadiust the duration of the following right of way period by changing the starting point of this timing period in accordance with the number of vehicles approaching the intersection against the It is also an object of this invention to provide a system in which the variation of charge in a condenser is instrumental in timing the "go" periods and in which vehicles approaching the intersection against the stop signal will pread- Just the timing of the following "go period thru varying in accordance with the number of such vehicles the initial charge in said condenser at the beginning of the said following "go period.

It is another object to provide an improved system in which the right of way will be automatically returned to a trafiic lane later if said right of way was last withdrawn from that lane by the maximum timer less than a predetermined time after the last trailic actuation of a detector in that lane.

It is still another object to provide a system in which the right of way will automatically be returned to a traific lane at the first reasonable opportunity if, when the right of way is withdrawn, the vehicle interval allotted to vehicles in that lane is thru the action of waiting cross traiiic or otherwise decreased to less than a predetermined time period.

Another object is to provide a system which can be arranged so that several adjacent intersections under this type of control will operate as a coordinated group or grid so as to facilitate the formation and passage of a large compact group of vehicles thru this group or grid in any path solely thru the pressure of traific without any electrical interconnection among the intersections.

It is also an object to provide a system in which ii desired certain forms of trafllc such as fire apparatus or trolley cars can have a multiple eifect in timing the signals so that one actuation by such a vehicle can have the same effect as several actuations by ordinary vehicles.

The invention is designed to encourage the closing up of scattered traillc which may wish to cross the path of dense traffic thereby effecting high efiiciency in the use of one intersection or a group of intersections. However such scattered tramc is never forced to come into close order unless the right of heavier cross trafilc requires this procedure. Hence the system operates to procure the greatest good to the greatest number without unduly sacrificing the right oi'any. I

The invention is exemplified in and will be particularly described in connection with the accompanying drawings, in which:

Figure 1 is a plan view of an intersection showing the location of trafiic detectors, signals and timer housing.

Figure 2 is a plan view of a group of adjacent intersections equipped with this system showing one example of the location of signals, traillc detectors and timer housings.

Figures 3 and 4 together comprise a circuit diagram of one form of apparatus embodving my nections to signals and traillc detectors.

Figures 5 and 6 show acircuit diagram for an alternative and in some respects preferred form of apparatus embodying my invention and employing a somewhat diiferent form of timing apparatus with its connection to signals and traiilc detectors.

Figure 7 is a schematic diagram of a form of special detector equipment by means of which preferred trafiic can exert a multiple eil'ect on the timing apparatus.

The traillc detectors for each intersection in the mesh or group shown in Fig. 2 are located at a considerable distance from the intersection so that the presence of a large group of vehicles can be detected for the purpose of according preference thereto as heretofore mentioned in the discussion of the coordination eflect of a group of non-interconnected intersections equipped with this system.

Any type of visual or audible signal can be used in this system but the customary red, yellow and green tramc lights are preferable inasmuch as motorists and pedestrians are now generally familiar with the significance of these colored lights.

The trafllc detectors may be of. any desired form such as a mechanical switch in which the pressure exerted by the weight of a passing vehicle flexes a resilient plate to make a contact, or anenergy beam is directed across a traflic lane so as to be interrupted by traffic approaching the intersection. A common form of the latter type is a light beam directed across a trafllc lane with a photoelectric cell arranged as a receiver. Still another type of detector is an electromagnetic device in which the vehicle disturbs a magnetic field and thereby operates a relay in the control. Any of these or other types of trafllc detectors such as a push button for use of pedestrians will operate satisfactorily in this system. i

The timer mechanism shown in Figs. 3 and 4 herein which controls the signals and is responsive to the trafllc detectors is of the type in which cams, fixed on a shaft which is revolved in steps by a solenoid with a ratchet and pawl mechanism or other suitable means, operate contacts to control the signal indications and to connect the various timing units in the timer circuit properly for the particular point in 'the signal cycle prevailing.

The cam shaft used in this system employs eight steps to complete one revolution which carries the signal indication thru one complete cycle, that is, from a go indication in one lane thru the go indication on the cross lane and thence back to the go indication on the first lane.

In the embodiment shown in Figs. 3 and 4 the timing of the various intervals is accomplished by means of apparatus including three element thermionic tubes arranged to be influenced by trafilc approaching the intersection.. A direct current relay is connected in the plate circuit of each tube in such a way that the plate current passes thru an operating coil of this relay. With constant plate voltage and constant plate external circuit resistance the plate current is controlled by the grid voltage of the tube in the man her usual in amplifier type thermionic tubes. With the grid markedly negative with respect to the filament substantially no plate current flows. If the grid voltage is made less negative the plate current increases.

Acondenserisincludedineachgridcircuit.

The voltage of each grid is controlled by the charge on the condenser associated therewith. when agrid condenser is sumciently charged. the plate current will become great enough to operate the relay thru which it Hence by controlling the starting charge and the rate at which charge is added to or subtracted from the grid condenser, each tube can be made to operate the relay associated with it at the end of a longer or shorter period.

. Figures 3 and 4 are complementary. In both figures the contacts identified by the capital letter C followed by a numeral are operated by cams mounted on a common cam shaft. This shaft is rotated by action of the solenoid 8 shown schematically in Fig. 4. The contacts identified by the letter 8 followed by a numeral are operated directly by the solenoid 8. Each time the solenoid rises in its stroke each of these contacts is changed from its normal condition of closed or open to the opposite condition. As the solenoid returns to its position of rest these contacts return to their normal unoperated conditions. Each cycle of operation of the solenoid including forward stroke on energization and return stroke on de-energization rotates the cam shaft through 45 degrees.

Eight steps of the shaft complete one revolution during which the signals 45 to ill inclusive in Fig. 3 go thru one complete cycle of changes, 1. e., from green in one street thru green in the cross street, back to green in the first street. The table at the bottom of Figure 4 indicates which ',cam contacts are closed in each of the eight positions of the cam shaft. An x in a square indicates that the contact whose number is at the top of the particular column including that square is closed when the shaft is in the position identified by the number at the end of the horizontal row passing thru that square.

The cam shaft positions are numbered from 1 to 8 as indicated in the table in Figure 4. When the cam shaft is in positions 1. 2 and 3 the green signal is displayed to N-S tramc, when in position 4 the amber or warning signal 46 is displayed to N-S traffic, and when the cam shaft is in positions 5, 6, 7 and 8 the red signal 41 is displayed to N-S traffic. The E-W green signal 48 is displayed while the cam shaft occupies positions 5, 6 and '7, the EW amber signal 49 is displayed in cam position 8 and the iii-W red signal 50 in cam positions 1, 2, 3 and 4. Other signal display sequences can of course be provided by this apparatus but this particular one is cited because it is in quite general use in tramc control systems.

In Figures 3 and 4 negative power is supplied thru the wire designated by a minus sign enclosed in a circle and a square which signifies a common grounded negative for both A. C. and D. C. Positive A. C. is supplied through wires designated by a plus sign in a circle, and positive D. C. thru wires designated by a plus sign in a square.

Referring to Figure 3, the apparatus represented by that part of the drawing to the right of the negative power wire is in general eiiective to cooperate with the apparatus of Fig. 4 to call the right-oi-way to the Er-W lane and to hold the right of way thereon. In like manner the apparatus represented by that part of Fig. 3 to the left of the negative power wire is effective to cooperate with the apparatus of Fig. 4 similarly to call or hold the right of way on the N-S lane.

At the topofFig. 3 areshownthetwo sets of.

signals representing the customary green, yellow and red lights, numbers 48 to ill being displayed to the E-W traiflc whereas numbers 4| to 41 are displayed to the N-S traiiic.

The traflic detectors located respectively in the N-S and E-W lanes are represented by II and D2. Relay E is responsive to actuations of detector II and relay F operates in response to actuatlons of detector II.

The operation of relay F starts a sequential operation which calls the right of way to the E-W lane and when the right of way has been given to the E-W lane, operation of this relay tends to hold it there. Similarly relay E operates to call and hold the right of way on the'N-S lane.

Relay M cooperates with relays E and F in calling the right of way as mentioned above and is also effective thru cooperation with relay A and a contact of solenoid S to cause right of way to return to a given la'ne later if, when right of way last left this lane the vehicle protection interval was shorter than a predetermined period, or if a detector was actuated thus initiating a new vehicle interval in this lane within a predetermined time previous to the yielding of the right of way to the cross lane.

Relay C cooperates with tube CT and condenser KC to time all the intervals which remain constant during successive signal cycles such as the amber period for each lane (cam shaft in position 4 or 8) and the maximum period during which trafllc can hold the right of way on either street against a cross lane call (cam shaft in position 3 or 'I). In addition if switch 69 is closed relay C, tube CT and condenser KC will cooperate to call the right of way to the E-W lane a predetermined time after said right of way last left the E-W lane, and closure of switch 68 will in a like manner cause relay C, tube (71 and condenser KC to call the right of way to the NS traflic lane a predetermined time after the right of way last left the N-Slane. This effect is termed the periodic call".

By opening or closing switches 68 and 69 the apparatus can be caused to normally operate as a reverting, arterial or floating system. The closure of both switch 68 and switch 69 will in the absence of tramc cause the right of way to normallyrevert periodically from lane to lane. This system of operation is commonly called the reverting system.

If switch BI is closed and switch 69 is open a N-S arterial system results in which the right of way will normally remain on the N-S lane until called by traiflc to the E-W lane. After the Er-W trams has cleared the intersection the right of way will automatically revert to the N-S lane. In the event of continuous E-W traili c under the above system the right of way will periodically revert to the N-S lane, and remain there as long as N-S traiiic may require it up to a predetermined limit.

If switch 69 is clowd and switch 8| open the system will operate arterial E-W under which system the E-W lane instead of the N-B lane will be the artery. The right of way will normally remain on the E-W lane until called by traflc to the 13-8 lane, from which lane it will revert to the E-W lane when the N-S trainc has cleared the intersection or has held the right of way on the N-S lane for a predetermined time.

If switches 68 and 89 are both open the apparatus will operate as a floating system under which the right of way will normally remain on the lane to which it was last called until tramc on the cross lane requires it.

Under all of these systems of operation tramc on each lane can hold the right of way up to a predetermined period against waiting trafllc in the cross lane and in addition automatically put in a call for the return of the right of way to the lane from which it is being transferred if at the time of such transfer a vehicle interval has been initiated by a detector actuation in said lane within a predetermined time prior to said transfer of the right of way or if the vehicle interval prevailing thereon at the time of such transfer has by waiting cross tramc been reduced to lws than a predetermined magnitude.

The cooperative action of relay C, tube CT, and condenser KC which time all intervals which do not vary from cycle to cycle is as follows: Condenser KC during each of these various intervals is being charged thru a fixed resistance, one of the several indicated in the right or left side of Fig. 3. As this charge increases the voltage of the grid ct! of tube CT to which condenser KC is connected increases. Hence the plate current of tube CT increases. when this current reaches a sumcient magnitude relay C operates which in turn operates the solenoid S to move the cam shaft into its next position.

In a generally similar manner tubes AT and BT are associated with condensers KD and KE and with relay B, which is a double coil relay, to time the initial and vehicle intervals which vary in their timing from cycle to cycle in accordance with the requirements of traflic. Coil b8 of relay B is its main operating coil. Boil b2,

'the bucking coil, is connected so that its magneto-motive force opposes that of coil b3 and therefore modifies the effectiveness of coil D3 to operate relay B. In order to insure that the bucking coil 112 shall under no circumstances operate relay B its magneto-motive force should always be less than that required to operate relay B or as an alternative said relay B might be of the polarized type in which case no limit need be placed on the magneto-motive force of coil b2. Current flows thru coil b2 only when the cam shaft is in position 3 or I, the NS and EW traflic timed positions, since in all other positions of the cam shaft the grid'of tube ET is biased negative to such a degree that substantially no plate current flows in this tube or in coil b2 of relay B.

With the cam shaft in position 3 or I the current thru the bucking coil M is regulated in accordance with previous actuations of the detector in the lane in which the stop" signal is displayed, in such a way that this current is caused to be less than a predetermined maximum by an amount substantially in accordance with the volume of the waiting cross traflic. This effect is the means by which waiting cross trafllc decreases substantially in accordance with its volume the timing of the vehicle interval in the lane in which the "go" signal is being displayed.

The current thru operating coil 113 when the cam shaft is in position 3 or 1 is affected by actuation of the detector in the lane in which the "go" signal is being displayed in such a way that a new vehicle interval is initiated for each actuation of a detector in this lane. Therefore itcanbeseenthatn'amcinbothlanesafl'ects the operation of relay B to time the vehicle interval for each lane in accordance with the trafflc requirements of both lanes.

Resistances RH and RI! provide by-passes around coil b! of relay B, which are adJus'table to control the effectiveness of tube BT in modifying the operation of relay B to the end that waiting cross traiiic can be caused to have a greater or less effect on the timing or the vehicle interval. 'In anetwork of intersections equipped with this system these by-pass resistances could be adjusted to a high value in order to increase markedly the effect of waiting cross traiii'c in decreasing the vehicle interval to aid in emphasizing the coordination effect naturally inherent in a group of adjacent intersections equipped with this apparatus.

Tube AT, as mentioned above, also cooperates thru the coil of relay A with coil b3 of relay B, condensers KE and KD, to time the initial intervals, cam shaft position I or 5, substantially in proportion to the number of vehicles waiting in the lane in which the go signal is displayed at the beginning of such interval. During the initial intervals coil b! of relay B carries no current due to the negative bias of grid bt2 of tube BT. Hence coil b3 alone is eflective to control relay B during the initial intervals.

Relay A is effective to cooperate thru solenoid and cam shaft contacts S2, C5, and C6 to operate relay E or relay F which will in turn operate the memory relay M to call the right of way to the lane from which it is being transferred if, at the time of such transfer, the vehicle interval prevailing on said lane is less than a predetermined 'time or if the right of way is transferred by' action of the maximum timer less than a predetermined time after a vehicle interval has been initiated by a detector actuation in said lane from which the right of way is being transferred. If either of these named conditions prevail relay A will be unoperated at the time the cam shaft moves into position 4. Therefore during this movement armature al of relay A thru its back contact and solenoid contact S2 complete a recall circuit" to operate the memory relay M and thus cause the right of way to return later to the lane from which it is being transferred just as if a vehicle detector in this lane had been actuated.

To more completely explain this system I shall now .describe in detail its operation to carry the signals thru one complete cycle.

Relay E is operable in all cam shaft positions upon actuation of the N-S vehicle detector which completes a circuit from negative power, thru detector SI and wire 58 to thecoil of relay E thence to positive power. Similarly relay F is operable in all cam shaft positions uponactuation of the EW vehicle detector 52 which completes a circuit from negative power thru detector 52 and wire 60 to the coil of relay 1'' thence to positive power. The effect produced by the operation of these relays is different in difl'erent cam shaft positions as will be pointed. out in the following description of the operation of the system.

Assume that the cam shaft is in position 2, called the NS rest position. The N-S go signal is energized thru wire 53 and cam contact C38. The EW stop signal is energized thru wire 58 and cam contact C38. Condenser KE which cooperates with tube AT and relay B to time the N-S vehicle interval is being charged thru the following circuit. Positive power thru resistance R4, contact CII, wires II and II to condenser Kill thence to negative power. While the cam shaft is in position I condenser K1: is subject to discharge at each vehicle actuation of detector II thru the operation of-reiay E. The subsequent recharge period. of condenser KE constitutes the vehicle interval for the thru the intersection of the vehicle in the, 31-8 lane which caused the operation of relay 1:. This discharge circuit for condenser KE goes from negative power to armature el of relay E, wires IQ, II, contact Cll, wires I! and thru condenser KE and thence back to negative power.

In this cam shaft position condenser KI: which asbefore mentioned cooperates with tube AT andrelayB totimetheN-S vehicle interval isconnectedtothe gridctIoftubeATthru wires 80, I! contact CI. and wire III. Hence the voltage of condenser K1? is effective to control the plate current of tube AT. This plate currentpassesthrucoilsofrelaysAandBthru a circuit starting at negative power. thru potentiometer resistance PI, wire III, filament atl and plate at! of tube AT to relay A thence thru wire II. to coil bl of relay 3 to podtive power. CoilblofrelayBcarriesnocurrentwhilethe camsha'ftisinpositionl sincethegridbtf'of tube ET is biased sufilciently negative with rerespeet to filament btl thru wires III, III and contact Cllto prevent any plate-current from flowing in tube BT.

When condenser KE is charged to a sufficient voltagetheplatecurrent oftubeATwhich passes thru coil b! will be great enough to operate relay B. When condenser KB has further charged to a still higher predetermined voltage the plate current of tube AT will further increase thus causing relay A to operate. While the cam shaft remains in position I- the operation of relay A or relay B is of no eifect since their armatures whether operated or not operated do not aifect any circuit. Relays A and B will however function when the cam shaft has moved into position 3 as will be explained later.

Movement of the cam shaft into position 3, called the N-S traihc timed position, is made in response to a cross lane call resulting either from a vehicle actuation of the E-W detector 52, or by action of the E-W periodic call circuit if the system is set to normally revert to the E-W lane, as would for instance be the case if the system were set to revert periodically from street to street or if the E-W lane were the main highway of an arterial system.

An E-W detector actuation will cause this cam shaft movement as follows: The operation of the E-W detector 52 will complete the circuit of relay 1" from negative power to positive power thru wire ill. The operation of relay F will energize relay M thru a circuit starting at negative power thru armature {3 of relay F, wires ill, 84, contact CII, wire 95 to coil of relay M thence to positive power. Relay M will thereupon operate and lock in thru the circuit starting at negative power thence thru armature mi of relay M,

wire 94, contact CI2 and coil of relay M to positive power. Solenoid S will now be energized thru a circuit from negative power thru armature ml of relay M, wire 94, contact Cll, wire I26, armature s5 and coil of solenoid S to positive power. Solenoid S wiJl therefore operate and cause the cam shaft to move into position 3.

With the system set to operate normally as a reverting or E-W arterial system switch is would resistance PI to negative power.

he closed so that if no actuation of an E-W vehicle detector takes place the cam shaft, after remaining in position 2 for a predetermined time. will be moved into position 3 by action of the periodic call circuit as was previously mentioned. The movement of the cam shaft to position 3 by means of the periodic call circuit is accomplished as follows.

With switch It closed condenser KC is charging while the cam shaft is in positions I or I thru the circuit starting from positive power thru switch 6!, contact C31, resistance R8, wires 81, I0, lill condenser KC to negative power. Condenser KC is connected to grid ct2 of tube 0'! thru wires I03. I02 and IM. Therefore when condenser KC has been charged to a predetermined voltage the plate current of tube CT will reach a magnitude suflicient to operate relay C thru its circuit starting at positive power thru the coil of relayC and wire I05, plate 03, and filament oil of tube CT, wire H2, potentiometer The, operation of relay C will complete the circuit from negative power thru armature cI of relay C, wire I25, 66, contact C29, wire 65, coil of relay F, thence to positive power. Relay F will now operate and cause relay M to operate solenoid S as before explained to move the cam shaft into position 3.

By adjusting the variable resistance R! the time required to charge condenser KC up to a voltage sumcient to cause the operation of relay 0 as above described can be made greater or less. Since condenser KC starts to charge when the cam shaft moves into position I .and E--W periodic call can be made to cause the cam shaft to move from position 2 to 3, at any predetermined time after the N-S lane is given the go signal unless E-W tramc has previously caused said transition. Resistance R3 in a similar manner regulates the timing of the N'S periodic call when the cam shaft is in position 6. It is by closing switches 88 and 69 and properly adlusting variable resistances R3 and R8 that the right of way as before mentioned can be made to normally revert at any desired intervals from street to street in the absence of trafllc.

As the cam shaft moves into position 3 contact Cl2 opens thus breaking the lock-in circuit for relay M which thereupon assumes its unoperated condition.

The operation of the solenoid S to move the cam shaft from position 2 to 3 is as follows. When the solenoid S is energized, as explained above, the core moves into the solenoid. The first effect of this movement is to change each of the solenoid contacts SI-SB from its rest'position in which some contacts are made and others open to the opposite condition wherein those contacts which were made when the solenoid was at rest are broken and those which were broken are made. As contact 85 opens the solenoid is deenergized but the inertia of the solenoid armature carries it beyond this point a considerable distance. At the top of the stroke a pawl engages the cam shaft ratchet so that on the down stroke the cam shaft is revolved thru 45 degrees. On the down stroke some cam contacts change before the solenoid contacts return to their normal positions and others change after in order to secure the proper sequence in the circuit changes occurring during this period of transition from one cam shaft position to another.

While the solenoid is operating to move the cam shaft from position I to 3 solenoid contact 83 completes a discharge circuit for condenser KC, which has been timing the periodic call period, to insure that no residual charge remains therein when condenser KC starts to time the maximum period in cam shaft position -8. As the solenoid returns to its unoperated position contact 83 opens this discharge circuit which may be traced from negative power thru contact 88, wire It, contact C1, wires I82, I88 to condenser KC thence back to negative power again.

While the cam shaft is moving into position 8 andwhile it remains there the circuits thru which relay A and coil I)! of relay B are energized, which have been previously described, remain as they were when the cam shaft was in position 2. As the cam shaft moves into position 8 relay B will have been operated if more than a predetermined period of time has passed since the last actuation of detector 51 and if relay B remains operated when the cam shaft has reached position 3 it will be effective to move the cam shaft on into position 4. However, as before mentioned, coil b2 of relay B aflects the operation of relay B in cam shaft position 8. This eii'ect will now be considered in-detail.

The magneto motive force of coil b2, as has been explained before, opposes that of coil bl. Hence the current which begins to flow thru coil b2 as the cam shaft movesinto position 8 may, if the current thru coil b3 has at that time reached a magnitude only slightly greater than that required to operate relay B without the opposition of coil b2, be sumcient to cause the armature of relay B to temporarily drop out. However the current thru coil b3 continues to increase if there are no N-S detector actuations. When this last named current reaches a sumcient magnitude it will overcome the opposition of coil b2 and cause relay B to again operate and move the cam shaft on into position I.

It is thru the effect of coil b2 on the operation of relay B that waiting EW cross tramc decreases the NS vehicle interval substantially in accordance with its volume. This is accomplished as follows:

The magnitude of the current thru coil b2 when the cam shaft is in position 3 is regulated in accordance with the number of actuations of detector 52 since the last display of the go signal in the EW lane, which is substantially a measare of the trailic waiting in the EW lane. This condition is brought about by connecting the grid N2 of tube BT to condenser KID in cam shaft position 8. As will later be explained in 'detail the charge on condenser KD at any time when the cam shaft is in position 8, l, 2, 2 or 4 is a predetermined charge, introduced when the cam shaft last moved from position 1 to 8, less the several increments removed thereafter in positions 8, I, 2, l and l by small condenser K2 in response to vehicle actuations of EW detector 82. Hence the voltage of condenser KD and therefore the voltage of grid M2 and consequently the plate current of tube ET, 1. e., the current flowing thru coil b2 of relay B, will be of a magnitude less than a predetermined value by an amount substantially in proportion to the number of actuations of detector 52 since the "go signal was last displayed in the EW lane. As

will be later explained in connection with the description of the circuits for reducing the voltage of condenser KD by increments by condenser K2 the amount of this reduction will be independent of the speed of invidual EW vehicles but will depend only upon the number of actuations by such vehicles.

Since a reduction of the current in coil b2 facilitates correspondingly the operation of relay B by the current in coil b8 a smaller current in coil b3 will be sufficient to operate relay B. A correspondingly smaller charge in condenser KE, which controls the current thru coil b3, will be sufficient to produce this smaller current in coil bl. Since this smaller charge will accumulate in condenser KE in a proportionately shorter period than would be required for a greater charge the vehicle interval being timed by this relay will, because of the sequential efl'ects described, be decreased in accordance with the reduction of the current in coil 112. Since the reduction of the current in coil b2 is, as above stated, in accordance with the volume of waiting EW cross traffic the reduction of the N-S vehicle interval will consequently also be in accordance with the volume of waiting E.W cross traihc.

The proportion of the plate current of tube BT passing thru coil D2 of relay B with the cam shaft in position 8 is regulated by adjusting resistance RH in order, as before mentioned, to increase or decrease the effectiveness of waiting EW vehicles to reduce the NS vehicle interval. The circuit including resistance Rll, wire 81, contact C26, and wire 88 accomplishes this effect by bypassing around coil b2 of relay B a proportion of the plate current or tube BT determined by the value of resistance R11.

The circuit for the charging of condenser KD during the movement of the cam shaft from posi-' tion 1 to 8 as mentioned above will be traced when the transition of the cam shaft from position 1 to 8 is described. The circuit by which this charge is diminished by vehicle actuation of EW detector 52 occurring while the cam shaft is in positions 8, I, 2, 3 or 4 is traced as follows:

When relay F is unoperated condenser K2 is charged from condenser KD thru the circuit starting from negative power thru potentiometer resistance P3, wire 16, condenser K2, wire 14, armature fl of relay F, wire 12, contact C25, wire 88, 8|, condenser E) thence back to negative power. An actuation of detector 52 will, as before explained, operate relay F which will break the last described circuit at armature ii of relay F thus disconnecting condenser K2 from condenser ICJ. Furthermore the operation of relay F will establish a discharge circuit for condenser K2 as follows, condenser K2, wire 14, armature f2 of relay F, wire 18, potentiometer resistance P8,and wire 16. As the vehicle releases detector 52, relay F becomes de-energized thereby breaking the discharge circuit for condenser K2 and reconnecting condenser K2 with condenser KD from which it will again be charged thereby removing another increment of charge from condenser KD. As indicated before, condenser K2 is of considerably smaller capacity than condenser KD and therefore each actuation of relay F by an EW vehicle reduces the charge and corresponding voltage of condenser KD by only a small increment. Also such reduction ofcharge on condenser KD by a series of EW actuations is arranged to take place on a relatively straight portion of the natural discharge-time curve of the condenser KD. Thus successive actuations reduce the charge on condenser KD by substantially the same amount and the total amount of reduction by a series of actuations is substantially proportionate to the number of actuations in such series. It will be appreciated that small condenser K2 will be substantially fully charged ach time it is connected to large condenser KD blsinceitisintendedmerelytoservetoflx the current required in coil bl to operate relay B. The more vehicles waiting in the E-W lane the lms will be the current in coil b2 when the cam shaft is in position [as previously explained. hence a correspondingly lower current is coil D3 will operate relay B. Since the charge in condenser KE which controls the current thru coil bl in cam shaft position 3 will be built up more quickly to the lower value required to produce this lower current in coil b2, the vehicle interval being timed thereby is therefore decreased substantially in proportion to the number of vehicles waiting in the E-W lane.

The circuit by which condenser ED is connected to grid M2 is from negative power to condenser KD, wire 9|, 9!, contact C23, wires I2! and III. Contact CIO thruwhich grid M2 is usually biased negative is open when the cam shaft is in position 3.

The circuit' by which relay B operates the solenoid S to move the cam shaft to position I is from negative power thru contact CSI, wire I28, armature bl of relay B, wire I26, armature s5 and coil of solenoid S to positive power.

While the cam shaft is in position 3 condenser KE is, as previously mentioned, subject to discharge by actuation of N-S detector I in order that each vehicle entering the intersection from the N-S lane may initiate a new vehicle interval to permit its passage thru the intersection. If vehicles in the NS lane approach at sufliciently short intervals they may by repeatedly discharging condenser KE keep its voltage so low. that tube AT will not at any time pass current enough to operate relay B. In order to insure that a continuous line of traillc in the N-S lane cannot thus indefinitely hold the right of way another means for moving the cam shaft into position I is provided in the maximum timer, the operation of which is not affected by tramc.

The maximum timer as before mentionedis comprised of relay C, tube (71, condenser KC and resistance R2. Relay C when operated in cam position 3 is affected to move the cam shaft into position l thru the following circuit, negative power, armature cI of relay C, wire I25, contact CH, wires I24, I26, contact s5 and coil of solehold 8 to positive power. Condenser KC is connected to grid ct2 of tube CT by wires I03, I02 and I, and is charged in cam position 3 thru a circuit from positive power, contact C, resistance R2 and wire ll. Resistance R2 is ad- Justed to charge condenser KCv at the proper rate to operate relay C a predetermined time after the cam shaft has moved into position 3 hence this timer circuit will be effective as a maximum timer to move the cam shaft into position I at the end of this predetermined period if continuous N-S trailic has prevented relay B from doing so earlier.

If relay A is unoperated as the cam shaft moves frompositionlto litwillputinaN-Sreturn anew is in its operated position preparatory to moving the camshaft into position I which it will do as it returns to its unoperated position.

Relay A will be unoperated and will therefore thru the above circuit put in a N-S return callas the cam moves into position I if as before stated the vehicle interval then prevailing has by walting E-W traillc or otherwise been decreased to less than a predetermined time, or if the last N-S vehicle interval was initiated less than a predetermined time before the said cam shaft transition to position 4 toohplace. In the above description of the two conditions under which a return call will be put in, the predetermined time mentioned is fixed by the operating period of relayA. Thiscanbeseentobe true becauseofthe following facts.

In cam shaft position 3 the operation of relay B, which times the vehicle interval, or of relay C, the maximum timer, will be effective to move the cam shaft on into position 4 and thus extinguish the NS go signal and illuminate the 11-8 amber or warning signal. If relay A operates before either relay B or relay C operates no N--S return call will be put in since contact al will be broken when the solenoid operates but if relay A does not operate before the cam shaft is moved into position 4 by action of either relay B or relay C a 11-8 return call will be put in during this transition. Whether relay A operates before or after relay B or relay C depends upon circumstances involving the following factors.

Relay A always operates when the current thru its coil reaches a predetermined value which, in cam position I, always occurs a predetermined time after the last vehicle actuation of a N-S detector. Relay B always operates when the difference between the current in coils b2 and b3 reaches a predetermined magnitude which condition occurs at a time after the last vehicle actuation of a N-S detector dependent upon the current in coil 12!. Henw, although the same current passes thru relay A and thru coil or of relay B, relay B may operate either before or after relay. A dependent upon the effect of the current flowing thru coil b2 on the operation of relay B. If the operating period of relay B by action of waiting cross tramc on the current thru coil b2 is decreased to less than that of relay A, thereturn call wilibe put in. But if the operating period of relay B is not so decreased and is consequently longer than that of relay A no return call will be put in if the cam shaft movement is caused by relay B. Hence the operating period of relay A constitutes the predetermined period below which the vehicle interval must be reduced by waiting cross traillc in order to put in cam shaft into position 4 condenser KB, preparatory to timing the next N-S initial interval and preparatory to decreasing the EW vehicle intervals in accordance with the waiting N-B cross traiiic, is charged to a predetermined voltage thru a circuit starting at negative power thence to condenser KE, wires 80, 02, contact CI, wire I", contact sl of solenoid 5, wire lllI, contact Cl, wire Ill, potentiometer resistance Pl to positive power. The voltage to which condenser KE is charged by this circuit can be regulated thru setting the point at which wire Ill makes contact with potentiometer Pl.

While the cam shaft is in position I, I, I, I or I the charge put into condenser KE as the cam shaft moved into position I is subject to diminution at each vehicle actuation of N-S detector II by'the amount required to charge condenser Kl which is discharged and recharged from condenser E once for each such actuation. When the cam shaft next reaches position I, the H initial interval position, the recharging period of condenser KE will time that interval thus causing it to be timed substantially in accordance with the number of vehicles waiting atthattimeintheN-Slane.

The circuit by which condenser KI diminishes the charge in condenser KE in response to N4 detector actuations is as follows. At each actuation of detector II relay E operates as previously explained. While relay E is operated condenser Kl is discharged to a predetermined voltage thru wire II, condenser KI, wire II, contact c2 of relay E and wire 11. The charge left in condenser Kl by this circuit is adjustable by setting the points at which wires II and 11 make contact with potentiometer resistance P2. Each time relay 1!. returns to its unoperated condition contact breaks after which contact el makes thus reconnecting condenser Kl to condenser KI: frmnwhicbitwillrechsrsethruwire'llcondenser Kl, wire 13, contact el, wire II, contact Cll, wires II, II, condenser KE thence back to negative power.

During the transition of the cam shaft from positlonttolcondenserKCisasaindischarged thru the circuit previously traced thru contact 01 and solenoid contact :3 preparatory to its use in timing the N-S amber period during whichperlodthecamshaftisinposition I. In this cam shaft position the N-B go signal circuit is opened by contact C38 and the N-B amberorwarningsignalcircuitis completedbycontact Cll.

While the cam shaft is in position I, the 11-8 amber position, relays A and B can not operate tomoveltintoposition I since the grids oftubes AT and B'! are biased sufliciently negative thru contacts Oil and Cl! respectively to prevent any plate current from flowing in these tubes which control the operation of relays A and B.

The timing of the N-S amber period, during whiehthecamshaftisinpositionl,isregulatedby the charging period of condenser KC which during this period is charging thru a circuit starting from negative power to condenser KC, wira I, II, resistance RI and contact CI! to positive power. The duration of the N-S amber period can be adjusted by varying resistance RI. When condenser KC is. charged to a predetermined voltage tube C1 will cause relay C to operate which will in turn thru a circuit previously described energize solenoid S to move the cam shaft into its next position, in this case position I, the EW initial interval pofltion.

While the solenoid S is operated to' move the cam shaft into position I the discharge circuit for condenser KC is again completed thru contact C1 and contact 83 in order to prepare this condenser for timing the next NS periodic call period which it will time while the cam shaft is in positions I and I, if switch 68 is closed as will be the case if the system is operating normally as a reverting system or an arterial system with the Ns lane the artery. The charging circuit for condenser KC in cam shaft positions I and 6 includes switch II,contact CII, resistance R3, wires 10 and I03. The charging period for condenser KC in cam shaft positions I and I can be regulated by varying resistance R3. When this condenser is charged to a predetermined voltage tube CT will operate relay C which will operate relay E thru contact C28 to call the right of way to the N-S lane.

In cam shaft position I contacts C39 and C open the circuit to the EW stop signal Ill and the N-S amber or warning signal II respectively. Contacts CII and C42 close to complete the circuits to the EW go signal 48 and the N-S stop signal 41 respectively. Contact C20 is open which disconnects grid atf of tube AT from negative power and contact C is closed to connect grid at! with condenser KD. Contact CII is closed in this cam position to complete a charging circuit for condenserlfl), thru resistance RIO, contact Oil and wires II, II. Thru this circuit condenser no will be recharged from the voltage to which it had been lowered by vehicle actuations of the EW detector while the cam shaft was in positions I, I, 2, 3 and I. This recharge period will be substantially in accordance with the number of such actuations thereby timing the EW initial interval in substantial accordance with the number of vehicles waiting in the EW lane at the beginning of this interval.

When condenser KD is so recharged to a predetermined'voltage tube AT will pass a plate current thru coil b3 of relay B sumcient to operate relay B to move the cam shaft into position I. The operation of relay B is not in this case affectedbycoilbibecausethegridoftubeB'Iis, as previously stated, biased negative thru contact CI! to prevent the passage of any plate current in tube BT. Because of the small current required in coil b! to operate relay B in the absence of opposition from coil b2, relay A does not operate. Moreover, if relay A did operate it would have no eflect since in cam shaft positions I and 8 its connection to relay E and F is broken by contacts CI and CI respectively.

As the cam shaft is by action of relay B moved into position I, condenser m) isdischarged to prepare it for timing the EW vehicle interval when the cam shaft is in positions I or I. This discharge circuit starts at negative power thence to condenser KD then thru wires II, If, contact Ci, wire I08, contact SI, wire III, contact C2, back to negative power.

Position 6 is the EW rest position Just as position 2 is the N-S rest position. Movement of the cam shaft from position I to I is accomplished, like the movement from position 2 to 3, only thru the operation of relay M. Relay M will have been locked in its operated position if a vehicle has actuated the 11-8 detector II since the go signal in the N-S lane was last extinguished or, as previously explained in describing theoperationof the apparatus when the cam shaft was in position I, if either of the following conditions prevailed when the cam shaft last moved from position 3 to 4:

1. If the right of way was last withdrawn from the Ns lane by action of the maximum timer relay C less than a predetermined time after the last actuation of a N-S detector. or

2. If at the time of this transfer the H vehicle interval had been by waiting E-W traflic to less than a predetermined minimum period.

If relay M has been locked as a result of the existence of any of the foregoing conditions it will be effective as soon as the cam shaft reaches position 6 to operate the solenoid to move the cam shaft on into position I thru the circuit which included armature ml and contact Cl! previously described in connection with the movement of the cam shaft from position 2 to I.

If relay M has not been operated when the cam shaft moves into position 4 this last named circuit will be open at armature ml and solenoid S will not be energized until relay 1! is subsequently operated by action of relay E which can be operated either from an actuation of 13-8 detector Si or from the action of the periodic call relay C to cause a normal reversion, the circuit for which has been previously described. Condenser KC which cooperates to time the periodic call is, with the cam shaft in position I or 0, charged thru the circuit including switch ll, contact C38 and resistance R3. The timing of this N-s periodic call, as before mentioned, can be adjusted by varying resistance R8.

As the cam shaft moves from position i to I condenser KC is discharged thru the circuit including contact 01 and armature s! of solenoid S to prepare it for timing the maximum period in cam shaft position I. The circuit of condenser KC, tube CT and relay C to time this maximum period is identical with that described in connection with the operation of the apparatus when the cam shaft is in position I except that the charging circuit for condenser KC includes resistance RI and contact CI! instead of RI and C34.

The E--W vehicle interval is timed in position I as the N-S vehicle interval was in position 3 except that the grid of tube AT is connected to condenser KD thru contact C24 instead of to condenser KE which makes the operation of the E-W detector 52 instead of the 8-8 detector 5! effective to initiate a new vehicle interval. Furthermore the counteracting effect of coil D2 of relay B is controlled by the voltage of condenser KE thru contact CII instead of by condenser KD, hence the waiting N-S traffic is effective to decrease the vehicle interval in cam shaft position I just as waiting E-W traffic decreased the vehicle interval in cam shaft position 3.

In cam position I resistance RI! thru contact C21 regulates the proportion of the plate current from tube BT flowing thru coil b2 whereby the magnitude of the effect of each N-S vehicle actuation to decrease the E-W vehicle interval can be controlled.

As the cam shaft moves into position by action of either relay B or relay 0 a return call to the EW lane will be put in if relay A is unoperated just as such a call was put in for the N-S lane when the cam shaft left position I if relay A was then unoperated. The circumstances under which relay A will be unoperated when the cam shaft moves from position I to l are identical with those which would cause it to be unoperated as the cam shaft moves from position I to 4 except that these circumstances pertain to conditions caused by E-W tramc instead of 11-8 traflic.

During the. transition of the cam shaft from position I to I condenser K1) is charged to a predetermined voltage which as before stated will incamshaftpositions 8, L2, land4bediminished by vehicle actuation of E-W detector 52 to prepare this condenser for decreasing the N-S vehicle interval when the cam shaft reaches position l and for timing the next E-W initial interval when the cam shaft reaches position i. The circuit thru which condenser ED is charged as mentioned during the transition position I to 8 is thru wires ll, 98, contact Cl, wire llll, armature SI, wire no, contact Cl, wire Iii to potentiometer resistance Pl The voltage of this charge is regulated by the point at which wire i I l makes contact with PI. The condenser KC is also during this transition discharged thru the circuit including contact 01 and armature SI in preparation for its use in timing the E-W amber period in cam shaft position 8.

In cam shaft position 8, the E-W amber signal position, E-W go signal 48 is extinguished thru the opening of contact C4l and the EW amber or warning signal 49 is illuminated by the closing of contact C43.

Condenser KC, tube CI and relay C co-operate, to time the E-W amber period as they do to time the N-S amber period which has been previously explained in detail. However, the charging circuit for condenser EC in cam shaft position I includes resistance R8 and contact C" instead of RI and contact C32 which are a part of the corresponding circuit in cam shaft'position 4. The duration of the E-W amber period can be regulated by adjusting resistance R8.

As the cam shaft moves from position 8 to I, condenser KC is again discharged thru the circuit including contact 01 and armature S3 to prepare it for timing the E-W periodic call which itwilldoincampositions l andlifswitch II is closed as previously explained.

The N-S initial interval, cam shaft position I is timed substantially in accordance with the number of waiting vehicles in the 11-8 lane by condenser KE cooperating with tube AT and relay B exactly as the E-W intial interval was, timed by the same tube and relay cooperating with condenser KD. Condenser KE, it will be remembered, was charged to a predetermined voltage as the cam shaft moved from position 3 to 4 i which charge has in cam shaft positions 4, 5, Q. I and i been diminished substantially in accordance with the numbr of vehicles actuating the 11-8 detector 5|. Hence, as previously explained, the duration of the NS initial interval which is governed by the time required to recharge condenser Kl: will be substantially in accordance with the number of vehicles waiting in the 17-8 lane at the beginning of this interval.

As the cam shaft moves into position I the 17-! amber signal 49 is extinguished by the opening of contact C41, and the N-S stop s gnal 4! is extinguished by the opening of contact C42. The N-S go signal 45 is illuminated by the closingof contact C", and the E-W stop signal I is illuminated by the closure of contact C39.

As the cam shaft moves from position I to 2 condenser Kill is discharged thru the circuit including contact C4, armature si and contact C2 to prepare it for timing the N-S vehicle in in cam positions 2 and I. p

The movement of the cam shaft into position 2 completes the'signal cycle.

Stated briefly, intervals are timed by this first embodiment of my invention by charging or discharging condensers KC, KD and KE. Condenser KC times those intervals which are unail'ected by tramc and do not vary from cycle to cycle.

The charge in condenser KD is influenced'by E-W trafilc actuations and is instrumental in timing the signal display periods in accordance with the requirements of EW trailic. The charge in condenser KE is similarly influenced by N-S traillc actuations and is instrumental in timing the signal display periods in accordance with the requirements of N-S trafllc.

During the N-S initial interval. cam shaft in position i, condenser E, which has since the last N'-S trafllc timed period been subject to the removal of unit charges by each NS trailic actuation, is now subject to regular charging action, not reset by actuation, to time the initial interval by recharging from" that point to which it has been discharged by such removal of unit charges.

During the E-W initial interval, cam shaft in position I, condenser KD functions similarly to time this interval.

During the N-S trafilc timed period of right of way, cam shaft position 3, condenser RE is subject to regular charging action to time this period and is subject to reset discharge by each N-S trainc actuation to extend this period by one vehicle interval. At the same time condenser KD, which is and has been since the last EW trafllc timed period subject to the removal of unit charges by each E-W trafllc actuation, serves to govern the length of such N-S vehicle interval.

During the E-W tramc timed period, cam shaft in position I, condensers KD and ICE perform similarly except that their functions are interchanged.

Another and in some respects a preferred embodiment of this invention is shown in Figs. 5 and 6. This second embodiment employs a rotary line switch instead of a cam shaft, and grid controlled discharge tubes instead of the amplifier type three element thermionic tubes. The use of the grid controlled discharge tubes makes it unnecessary to employ a double coil relay to permit waiting cross trafllc to decrease the vehicle interval as will subsequently be explained. Furthermore because of the sharply defined "breakdown" voltage of this type of tube great accuracy is pos sible in timing the various intervals. Moreover since their grid potential determines their "breakdown" voltage the circuits involving these tubes can be adjusted to compensate for variations in tube characteristics by connecting the grid to an appropriate potentiometer tap when tubes are replaced. Thus the accuracy of the timing of the various intervals can be maintained independent of variation of tube characteristics in diflerent replacement tubes.

The stepping switch shown in Fig. 5 has eight positions just as did the cam shaft of Figs. 3 and 4. A stepping switch of more than eight positions can be used as an eight position switch if desired by providing rapid stepping thru the extra positions in accordance with well known methods.

The various time intervals correspond substantially in both embodiments. In this second embodiment as in the first the initial interval is timed substantially in accordance with the number of waiting vehicles by charging a condenser during that interval from an initial voltage predetermined by the amount of said waiting trafllc.

When the stepping switch is in its trafllc timed positions 8 or 1, three timers run concurrently. One of these, the maximum timer, is not subject to vehicle control. The other two, the variable vehicle interval timer and the normal vehicle interval timer, are both subject to reset thru plate condenser discharge by trafllc actuations in the lane in which the go signal is being displayed. Hence their periods start simultaneously after each such reset. The variable vehicle interval timer is subject also to partial control by waiting cross traflic which decreases its operating period. The normal vehicle interval timer on the other hand is not affected by cross trafllc.

The variable vehicle interval timer period is decreased by waiting cross traillc thru having the grid potential of the tube timing this period rendered less negative by waiting cross traflic thus causing said tube to become conducting at a lower plate voltage which correspondingly decreases the period required for charging the plate condenser to this lower voltage and so decreases correspondingly the variable vehicle interval. Hence the larger the amount of waiting cross trafllc the shorter the variable vehicle interval will be. From the above description it can be seen that the variable vehicle interval timer in effect balances the increasing pressure to take the right of way exerted by accumulating waiting trafilc on one street against the right of way retaining effect exerted by moving trafllc on the other street. The latter eflect may be termed the holding power" and is proportionate to the frequency with which said moving trafllc resets the variable vehicle interval timer, since moving traflic having the right of way will reset this timer at a higher time frequency as the time spacing between actuated vehicles is reduced in the moving stream of trafllc, or in other words as the vehicles become more closely spaced. The closer the spacing of vehicles is in the stream of trafllc moving with the right of way the shorter is the time interval between vehicles in which condenser KVV is allowed to charge, and the lower is the maximum voltage condenser KW is allowed to reach, so that such trafllc tends to hold the condenser voltage below the "break down" of tube WT and thus to hold the right of way. This "holding power" is opposed by the action of trailic approaching at a distance on the opposite street. which does not have the right of way and on which approaching trafllc stops as it reaches the intersection. Each actuation by vehicles of the latter traffic reduces the negative grid bias on tube VVT and thus reduces its "break down voltage, so that condenser KVV voltage does not have to rise so high to operate tube WT and cause release of right of way.

If the variable vehicle interval is decreased to less than the normal vehicle interval right of way will be yielded by action of the variable vehicle interval timer when traillc ceases to approach the intersection from the lane in which the go signal is being displayed. The variable vehicle interval timer is arranged to automatically put in a return right of way call whenever it operates to yield right of way. If there is little waiting cross traillc and consequently the variable vehicle interval is not reduced to less than the normal vehicle interval, the normal vehicle interval timer will operateflrst to yield the right of way. The operation of this timer does notputinareturnrightofwaycall. Hence? in the second embcdlment of my invention as in the first, a right of way recall will be automatically put in if the vehicle interval at the time of right of way transfer has been reduced by waiting cross traffic to less than a predetermined period. In this second embodiment shown in Figs. 5 and 6 the predetermined period" referred to is the normal vehicle interval timer period whereas in the first embodiment shown in Figs. 3 and 4 the corresponding predetermined period is-the normal period for charging the timing condenser to the voltage necessary to operate period of relay A. This charging period will be greater than that for operation of relay B in the presence of any considerable amount of waiting cross traific. I

If repeated trafilc actuations in the lane in which the go signal is being displayed continually reset both of the vehicle interval timers thus preventing either of them from operating the right of way will be transferred by action of the maximum timer, which is efi'ective in the traific timed stepping switch positions I or 1. A return call for the right of way is automatically put in by this timer whenever it operates.

The fact that the maximum timer operates and the normal vehicle interval timer does not operate indicates thatthe normal vehicle interval timer was reset by a trafilc actuation less than the time period of said normal vehicle in-- terval timer, 1. e., less than a predetermined time before the transfer 'of the right of way. It will be remembered that this is one of the conditions under which the embodiment of Figs. 3 and 4 also is arranged to automatically put in a return right of way call, the predetermined time" in that apparatus being the time period of relay A. Hence both embodiments fulfill this condition.

The stepping switch, like the cam shaft of the first embodiment, will remain in either of its two rest positions 2 or 8 unless the system is set for normally arterial or reverting operation or unless a cross trafllc call is put in by a cross lane detector actuation.

Referring to Figs. 5 and 6 the following points will be noted. Those elements in Figs. 5 and 6 which correspond closely with specific parts shown in Figs. 3 and 4 are designated in Figs. 5 and 6 by the same number or letter used in Figs. 3 or 4 with the letter Z added, as .for example the signals in Fig. 3 are numbered 45 to inclusive and in Fig. 5 are designated as Z45 to Z" inclusive.

The stepping switch contact banks, designated as SBI to 838 inclusive, are shown in Figs. 5 and 6 to the right of the grounded power wire which extends from the bottom to the top of both figures just to the left of the center. The stepping switch driving magnet, designated as DM, is shown in the lower left comer of Fig. 6. This magnet DM drives the wipers WI to W6 in unison over the banks SBI to BB8 respectively. Beside it is a rectifier used to supply D. C. for the driving magnet coil.

The signals shown at the top of Fig. 5 are controlled by relays ALR and BLR. The apparatus to the left of the grounded power wire in Fig. 5 is in general effective to co-operate with the apparatus of Fig. 6 to call and hold the right of way on the N-S lane whereas that to the right of the grounded power wire similarly "cooperates with the apparatus of Fig. 6 to call and hold the right of way on the EW lane.

Relay AM is energized thru contacts in stepping switch bani: 832 when the stepping switch is in positions 2 and 3, the N-S rest position and the N-S trafilc timed positions respectively. Right of way can be called to the N-S lane by the de-energization of relay AM which can occur in response to a NS trafilc actuation when the right of way is not on the N-S lane. Furthermore if the right of way leaves the N-S lane thru action of the maximum timer relay MXR or the variable vehicle interval timer relay VVR the relay AM will be de-energized thus putting in a call for the return of the right of way to the lane from it is being withdrawn, in this instance the N-S lane. It will be remembered that the placing of a return call has been mentioned as a function of both the maximum timer. and the variable vehicle interval timer.

If on the other hand the right of way is transferred from the N-S lane by action of the normal vehicle interval timer relay YR, relay AM will not be de-energized but will remain locked in thru subsequent stepping switch positions unless it is de-energized by the actuation of a 11-8 vehicle detector in order to call the right of way to the N-S lane.

Relay BM performs similarly with respect to the E-W lane, being operated thru contacts of stepping switch bank SBI when the stepping switch is in position 0 or I, the E-W rest and trafilc timed positions respectively. It is deenergized to put in an E-W return call as the right of way is withdrawn from the E-W lane if said withdrawal is caused by the maximum timer relay MXR or the variable vehicle interval timer relay VVR. but remains locked in if said withdrawal of the right of way is caused by the operation of the normal vehicle interval timer relay YR. Relay BM in subsequent stepping switch positions can be de-energized by action of relay FZ in response to an actuation of iii-W detector Z52 in order to call the right of way to the E-W lane.

Relay AR which is energized by stepping switchcontacts of bank SBI in stepping switch positions I, 2, 3 and 4, the NS right of way and amber positions, energizes signal relay ALR and completes certain of the timing condenser circuits as will later be explained in detail.

Relay BR is energized in stepping switch positions 4, 5, I and 1 to similarly energize signal relay BLR and connect other timing condenser circuits.

The maximum timer. effective in the N-S and E-W trafiic timed stepping switch positions 3 and I to limit the time during which moving trafilc can hold the right of way against waiting cross'trafilc, includes relay MXR, plate condenser KMX and tube MXT.

The variable vehicle interval timer includes relay VVR, tube WT, plate condenser KVV and grid condensers KGNS and KGEW. It times the variable vehicle intervals in stepping switch positions I and I, the charge in condensers KGNS and KGEW being affected respectively by E-W and N-S trafilc so as to decrease the variable vehicle interval in the 11-8 and E-W lanes respectively in accordance with the amount of waiting cross trafilc as previously mentioned.

Relay YR, tube YT and condenser KV cooperate to time the normal vehicle interval, with the stepping switch in position 3 or I, which interval starts simultaneously with the variable vehicle interval after each vehicle actuation in the lane having the go" signal. The timing of the normsivehicieintervalitwiilberememberedisnm ailected by waiting cross tramc whereas the timing of the variable vehicle interval is aifected by waiting cross traillc.

RclayYRandtubeY'l'cooperatewithother condensers in diil'erent stepping switch positions to time other intervals as follows. The N-S initial interval. stepp ng switch position I, is timed by relay YR. tube YT and condenser KINS, the charge in condenser ms at the beginning of this interval having been predetermined by 11-8 vehicle actuations occurring during or before the preceding display of the N-S stop aim] in order to time the N-S initial interval in accordance with the amount of N-S tramc waiting at the beginning of the 11-8 go signal display period.

Relay YR and tube YT cooperate similarly with condenser KIEW to time the E-W initial interval, stepping switch in position I, in accordance with the amount of E-W tramc waiting at the beginning of the E-W go" signal display period, the starting charge in condenser KIEW being predetermined in accordance with the amount of said waiting E-W tramc.

The same relay and tube cooperate with condenser KY to time a minimum period during which the stepping switch remains in its rest positions 2 and I in order to ensure that when the "go" signal is given to a lane it will remain there for a reasonable minimum period. At the expiration of said minimum period the right of way will be transferred to the other lane only if trailic or normal reversion requires it, hence the name "rest position". This same group times the N-S and E-W amber or warning periods, stepping switch in positions I and 8 respectively.

To more completely describe the features of the I embodiment of my invention shown in Figs. 5 and 6 I shall now explain its operation thru a complete signal and stepping switch cycle beginning in the N-S initial interval when the right of way has just been given to the NS lane, stepping switch in position I.

In this stepping switch position relay AR is operated. current being supplied thru the circuit starting at grounded power thence thru position I of stepping switch bank SBI to relay AR to A. C. plus power. Relay AR when operated causes signal relay ALR to be energized thru the circuit starting at A. 0. plus, thru relay ALR, wire 202 to contact or! of relay AR thence to grounded power. Relay BR is de-energized in stopping switch position I, its circuit being open at stepping switch bank 532. 31-8 is de-energised since its operating circuit includes contact In! of relay BR.

WlpersWI andw2areofthe bridgingtypeso that the relays energized thru them at their respective contact banks EDI and as: will not be de-energiaed as the stepping switch moves from one position to the next.

With relay ALR operated and relay BLR unoperated the N-S so B snal Z46 will be illuminated thru the circuit beginning at grounded power. thru signal Z4! thence to contact blrl of relay BLR thence to connect alrl of relay ALR and to A. C. plus power. The EW stop signal ZII is illuminated thru the circuit from grounded power to A. 0. plus power including signal ZII and contact 011-2 of relay ALR. 'l'he circuits to the other four signals are incomplete in stepping switch position I.

Explanation of the relay AM coil circuit will be helpfulatthispointasanaidinfollowingthis stepbystepdescription oi'the systemoperation.

Relay AM has an operating circuit from grounded power thru wiper W2, stepp n switch bank 882 positions 2 and I, wire III, III, coil of relay AM, wires III, Ill, 2'", 22!, contact d1n2 toA.C.plus. Ithasin additionaholdingcircuit fromgroundedpowerthrucontactezlofrelay EZ, contact curl of relay AM, wire 2.5, coil of relay AM, wires 2, 21', 211 to contact m2 of relay AM, wire 2". contact mzrl of maximum timer relay m, contact curl of variable vehicle interval timer relay VVR, thence to A. 0. plus power.

In stepping switch podtion 2 relay AM is energized thru the operating circuit described above. That part of the operating circuit supplying current to the left side of the coil remains complete from the time the stepping switch enters position 2 until it leaves position I after which it is broken at bank 832. Wiper W2 is of the bridging type to insure continuity of the above circuit as the stepping switch moves from position 2 to I.

Thatpartoftheoperatingcircuit the right side of the coil of relay AM will be opened at contact dm2 as the stepping switch moves from position 2 to I. However that portion of the holding circuit paralleling the last named part of the operating circuit remainsintact to supply relay AM with A. C. plus power while contact dm2 is open during the stepping switch movement. From the above description it can be seen that relay AM is always energized when the stepping switch is in position 2 or I and when it is moving from position 2 to position I.

The functioning of relay AM in subsequent stepping switch positions will be explained as the circuit operation in each position is considered.

The N-S initial interval is timed by re ay YR. tube YT and condenser KINS. During this interval condenser ms is connected to relay YR and to the plate of tube Y'l thru the circuit going from grounded power to condenser KINS to wires 2", III, 2 to stepp s switch bank SBI position Ito wiper WI, wires 224, 225 to coil of relay YR. wire 2" to plate of tube YT. During the N4 initial interval condenser KINS is charged thru the circuit starting at grounded power, to condenser KINS. wires "2, 2, 2, to stepping switch bank SBI pomtion I to wiper WI, wires HI, I to timing resistance RZI. wire 2, to stepping switch bank 834 position I, to wiper WI, wire 22 nect the rectifier associated with the driving magnet DM to power thusenergizing the stepping switch driving magnet DM which will thereupon move the stepping switch into its next position. To vary the duration of the NS initial interval the rate at which condenser KINS is charged in stepping switch position I can be adjusted by regulating the variable charging RZI.

It has previously been stated that the initial interval is by the apparatus of Figs. 5 and 6 as well as by that of Figs. 3 and 4 timed substantially in accordance with the amount of waiting crosstraflicthruhavingthechargeintheinitial interval timing condenser at the of the initial interval predetermined by such waiting cross traillc. In this connection consider me cincally the N-.-S initial interval during which the stepping switch is in position I.

While the stepping switch was last in posi 2 andirelayAMwasenergizedashasbeen viouslyexplained. Therefore in these two ping switch positions condenser ms charged thru the circuit irom grounded power to condenser ENS, wires 28!, Ill, contact aml oi. relay AM, to resistance RZII, wire III to popotentiometer PZ'I to which wire 2!. is attached. The rate at which condenser KINS is so charged can be regulated by the adjustment of variable resistance RZI I. I

While condenser KINS was being charged in stepping switch positions 2 and i as explained above and during succeeding intervals up to the E-W amber period immediately preceding the actuationseven during the 11-8 go signal display period provides a means whereby those N-S vehicles which, under heavy trai'llc conditions. are

- stopped byloss oi right of way after having actuated the 11-8 detector make their presence eiiective to increase the next N-S initial interval.

The removal of increments oi charge irom condenser KINS is accomplished thru the iollowing circuit including contacts of relay EZ. 0ondenserKINSis connectedtocontactesl oirelsy EZ thru contact am! of relay AM in stepping switch positions 2 and I and thru contact Dr! 0! relay BB. in stepping switch positions 4, I, e and I. Hence in all oi these named stepping switch positions actuaticns of 11-8 detector III which operates relay EZ will cause contact es! and eat to cooperate to remove an increment of charge from condenser KENS just as contacts el and e! did in the embodiment of my invention shown in Figs. 3 and 4.

The charge so removed irom condenser KINB by waiting N-S traihc is replacedthru resistance RZG during the initial interval thus timing said initial interval in accordance with the amount of such waiting N-S trafllc. When condenser KINS is so recharged, i. e., when the 11-6 initial interval is over, tube YT becomes conductive and condenser KINS discharges thru relay YR which thereupon operates. The stepp switch. as previously explained, thereupon moves on into position 2, the N-S rest position. During the movement of the stepping switch from position I to 2 condenser KY is discharged thru driving magnet contact dm! in preparation for its use as a timing condenser in stepping switch position 2.

It the system is not set for normal reversion to the E-W lane and there is no waiting E-W traflic the stepping switch will remain in this N-S rest position and the N-S lane will be continuously accorded the go signal \mtil an E-W trafllc actuation shall occur.

In stepping switch position 2, the N-S go signal rest position, relay YR, tube YT and condenser KY time a predetermined minimum periodattheendoiwhichthe mnin switchcan bemovedoninto positionIeitherbyanE-W traflic actuation or by normal reversion.

The circuit connecting relay YR,'tube YT and condensei-KYinsteppingswitchpositionl isas thru wires III, 224, wiper I of bank BB! is connected to KY thru wires 22! and III. In addichargiug cir t-is established for con- KY starting at grounded power to con- KY, to wires I58. I28, position 2 of bank 833, wiper W3, wires I24, 223, adjustable re- RZII, wire ill. position 2 of bank 834,

Ill, contact dml of driving magnet DM to us power.

Wiper W8 is or the non-bridging type so that the stepping switch moves from one position the next there will be no interconnection oi condenser circuits. Contact dml is included in the charging circuit described above to prevent sag iii

Egg

irom one stepping switch position to another.

The timing of the N-S minimum rest position period can be adjusted by regulating resistance stepping switch position I.

grid cirguitni" tube YT in steppi switch lls connected thru wire 2", wiper WI iiositim 2 of bank 8B5. wire "I to potentiometer PZI. Wiper WI is of the bridging type to prevent fluctuations in grid potential as the stepping switch moves from one position to the It will be noted that the'resistance P21 and and minus power terminals, and that the JunctionpointoiPZl and Pztisconnectedtothe central vertical ground wire, thus providing a potentiometer arrangement in which ground potential and the left end of PZO are more positive than the right end. and various points on P2! may be tapped for different negative voltages with respect to ground. P24 and P2! are adapted to be individually connected between D. 0. minus and grolmd. and when either is so connected it provides a potentiometer across the resistance P28. The negative end or potentiometer P25 is permanently connected to D. C. minus but thepositive end of P25 is connected to ground thru a circuit including wire 2 and contact Inn of relay BM or E-W arteriaLswitch ZN. Hence it both switch Z and contact bml are openthepotentialoithegridoitubeYTwillbe biased negative to such a degree that said tube will not break down even through plate condenser KY be charged to its maximum positive voltage. Therefore with contact bmB and switch Z open the stepping switch will remain at rest in position I even after condenser KY has become i'uily charged.

The above condition prevails ii the system is not set for normal reversion to the E-W lane and there is no waiting E-W trafllc. Under these conditions the stepping switch remains in position 2, its N--S rest position, and the go signal continues to be displayed in said N-S lane until the next E-W trafllv actuation occurs.

It normal reversion to the E-W lane is desired switch Z is closed which will make the grid potential of tube YT less negative so that the tube will "breakdown" and operate relay YR. causing the stepping switch to move from positionltolassoonascondenserKYissuito control the chargingrate oi condenser fllciently charged, 1. e.. at the expiration of the stepping switch position 2 minimum period. If switch Z" is not so closed the movement of the stepping switch from position 2 to 3 will take place at any time after the expiration of said minimum period upon actuation oi the EW detector Z32 which wfll de-energize relay BM by opening its holding circuit at contact jzl of relay F2. The de-energization of relay BM causes contact bml to complete a circuit connecting potentiometer-PZI to ground thus making the grid potential of tube YT much less negative so as to cause the tube to "break-down and relay YR to operate, causing the stepping switch to move from position 2 to 3. If an actuation of detector Z32 takes place before the expiration of the rest position minimum period said stepping switch movement will take place at the end of this minimum period.

In stepping switch position 3 the N-S go signal and the EW stop signal remain displayed and three timers, the normal vehicle interval timer, the variable vehicle interval timer and the maximum timer run concurrently. The first two of these timers are subject to reset by N--S detector actuations and the timing period of the variable vehicle interval timer is in addition shortened by waiting EW traillc in, accordance with the amount of such waiting EW tramc. The maximum timer is not aflected by traiilc in either lane and sets a maximum limit beyond which N-S trafllc cannot continue to hold the right of way against the cross lane.

The normal vehicle interval timer includes relay YR, tube YT and condenser KV. The grid of tube YT is in stepping switchposition 3 connected to potentiometer PZB thru position 3 of bank 83!. The circuit from relay YR. to wiper W3 of bank BB3 has been traced. Thru this bank, in position 3, condenser KV is connected to relay YR by wires 23!, 232, 233 and 234.

Condenser KV. while the stepping switch was in positions I and 2, was being charged thru a circuit including grounded power to condenser KV, wires 23, 233, 232 and 230 to variable resistance RZI'I, wire 23! contact art of relay AR to positive D. C. power. In stepping switch positions I and 2 condenser KV was also subject to discharge by N-S detector actuations thru contact eel of relay EZ, wire 231, contact ar2 of relay AR. to ground. Ii, when the stepping switch enters position 3. the trafllc in the N-S lane has cleared the intersection condenser KV will have had sufllcient time since the last NS detector actuation to become fully charged. In stepping switch position 3 condenser KV is connected to the plate of tube YT. Hence if this condenser is fully charged when the stepping switch moves into position 3 tube YT will immediately break down and operate relay YR to move the stepping switch on into position I with no appreciable stop in position 3. If on the other hand N-S detector actuations have recently discharged oondenser KV the normal vehicle interval timer willcontinueitstimingaslongasthe stepping switch remains in position 3.

The variable vehicle interval timer includes relay tube WT, plate condenser KW and, in stepping switch position 3, grid condenser KGNS. In stepping switch position 3 plate condenser KVV is charged thru a circuit from grounded power to condenser KW. wire 203, 2", 222, 22L 223, variable resistance R24, wire 2l2 to position 3 of bank 834, wiper W4, wire 223, contactdml toD.C.pluspower. WiperWlisof the non-bridging type to prevent interconnection of charging circuits during stepping switch movement. Contact dml is included in this circuit to prevent tube flashover during the stepping switch movement as has been explained before.

Condenser KW is subject to discharge upon actuation of N-S detector ZGI thru the circuit from grounded power to contact art of relay AR to contact ezli of relay EZ thru wire 240 which ties into the condenser KVV charging circuit at wiie 222. The grid of tube WT is connected to condenser KGNS thru the circuit including wire 249, contact hr! of relay BR and wire 246 to condenser KGNS, thence to ground. The charge of condenser KGNS has in previous stepping switch positions been made less negative by the removal of increments of charge by condenser KBNS, one increment of charge being removed for each actuation of EW detector Z52, so that the charge on condenser KGNS when the step-' ping switch is in position 3 has been reduced in accordance with the amount of waiting EW trafllc.

The circuits which accomplish the above results are as follows: In stepping switch positions 6 and I condenser KGNS is charged negatively thru the circuit from grounded power to condenser KGNS, wires 2, 2", contact bmb, variable resistor RZZiI, wire 25! to potentiometer PZ6. The point at which wire 255 makes contact with potentiometer PZ6 fixes the maximum negative potential to which condenser KGNS can be charged by this circuit. The rate at which this charge takes place can be regulated by adjusting resistance R220.

The removal of increments of charge from condenser KGNS is accomplished as follows. In all stepping switch positions condenser KBNS is charged by condenser KGNS and then discharged to a predetermined potential once for each actuation of EW detector Z52. This detector operates relay FZ whose contacts 126 and {21 are effective to accomplish the above as follows. With'contact fzl closed condenser KBNS is discharged to a predetermined voltage thru the circuit including grounded power. condenser BN8, wire 24!, contact fzl, wire 25!! to potentiometer F26. The voltage to which condenser KBNS is so discharged is regulated by setting the point at which wire 250 contacts potentiometer PZG. A vehicle actuation of EW detector Z52 opens this discharging circuit at contact 121 and connects condenser KBNS to condenser KGNS thru the direct circuit including contact I26. The voltage on condenser KBNS, which was regulated to be less negative than that of condenser KGN'S, will therefore cause the voltage on condenser KGNS to become less negative. Hence, when the stepping switch reaches position 3 the charge in condenser KGNS will have been reduced in accordance with the total of all the increments removed by condenser KBNS in response to EW traflic actuations and substantially in accordance with the number of such EW actuations since the right of way last left the EW lane.

The fact that increments of charge are removed from condenser KGNS in response to EW trafilc actuations even during the EW go signal display period provides a means whereby those EW vehicles which, under heavy trafflc conditions, are stopped by loss of the right of way after having actuated the EW detector make their presence felt in decreasing the next NS variable vehicle interval timing by means which will now be explained. 

